The present application relates to an image display apparatus used to allow an observer to view a two-dimensional image formed by an image forming device and so on.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-521099 and Japanese Unexamined Patent Application Publication No. 2006-162767 disclose virtual-image display apparatuses (image display apparatuses) in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device.
FIG. 1 is a conceptual view of such an image display apparatus. Referring to FIG. 1, an image display apparatus 700 (referred to as an image display apparatus 700 of a first type for convenience and denoted by reference numeral 100 in FIG. 1) includes an image forming device 711 (111 in FIG. 1) having a plurality of pixels arranged in a two-dimensional matrix, a collimating optical system 712 (112 in FIG. 1) for collimating light emitted from the pixels of the image forming device 711, and an optical device 720 (120 in FIG. 1) on which the light collimated by the collimating optical system 712 is incident. The incident light is guided and emitted from the optical device 720. The optical device 720 includes a light guide plate 721 (121 in FIG. 1), a first optical member 730 (130 in FIG. 1, for example, formed by a single-layer light reflective film), and a second optical member 740 (140 in FIG. 1, for example, formed by a light reflective multilayer film having a layered structure. Incident light propagates in the light guide plate 721 by total reflection and is then emitted from the light guide plate 721. The first optical member 730 reflects the light incident on the light guide plate 721 so that the incident light is totally reflected in the light guide plate 721, and the second optical member 740 emits the light, which propagates in the light guide plate 721 by total reflection, from the light guide plate 721. For example, when a HMD (Head-Mounted Display) is produced using this image display apparatus 700, the weight and size of the display can be reduced.
Further, Japanese Unexamined Patent Application Publication No. 2007-94175 discloses a virtual-image display apparatus (image display apparatus) using a hologram diffraction grating, in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device.
FIG. 4A is a conceptual view of such an image display apparatus. Referring to FIG. 4A, an image display apparatus 800 (referred to as an image display apparatus 800 of a second type for convenience and denoted by reference numeral 300 in FIG. 4A) basically includes an image forming device 811 (111 in FIG. 4A) for displaying an image, a collimating optical system 812 (112 in FIG. 4A), and a virtual-image optical system (an optical device 820, denoted by reference numeral 320 in FIG. 4A) on which light displayed by the image forming device 811 is incident. The incident light is guided to the eye 10 of the observer. The optical device 820 includes a light guide plate 821 (321 in FIG. 4A), and a first diffraction grating member 830 (330 in FIG. 4A) and a second diffraction grating member 840 (340 in FIG. 4A) that are provided on the light guide plate 821. Each of the first and second diffraction grating members 830 and 840 is formed by a reflective volume hologram diffraction grating. Light emitted from the pixels in the image forming device 811 enters the collimating optical system 812, where the light is converted into parallel light, and the parallel light enters the light guide plate 821. The parallel light is incident on and is emitted from a first surface 822 (322 in FIG. 4A) of the light guide plate 821. On the other hand, the first and second diffraction grating members 830 and 840 are mounted on a second surface 823 (323 in FIG. 4A) of the light guide plate 821 parallel to the first surface 822.